Chromatic Aberration

Vignetting

Geometric Distortion

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Buy the Pentax 50-200mm f/4-5.6 ED SMC P-DA

(From Pentax lens literature) Designed for exclusive use with Pentax KAF-mount digital SLR cameras, the new lens offers 4X zoom coverage in the telephoto range.

Note: a less expensive "L" version of the lens is available bundled with some bodies. L version lenses have a plastic lens mounts, don't not include a lens hood, and do not support Pentax's Quick Shift Focus System. Optically, they are identical.

SLRGear ReviewApril 16, 2008by Andrew Alexander

Released in 2005, the Pentax 50-200mm ƒ/4-5.6 ED SMC P-DA represents the consumer end of Pentax's telephoto zoom lens offerings.

The lens is designed to fit the digital APS-C sensor, but I didn't find any evidence of corner vignetting on a film body until 135mm or longer. It's also a variable aperture lens, in that as you increase the focal length, both the maximum and minimum aperture sizes decrease. The following table reflects the change in aperture with focal length:

Focal Length

50-63mm

64-149mm

150-200mm

Largest aperture

ƒ/4

ƒ/4.5

ƒ/5.6

Smallest aperture

ƒ/22

ƒ/29

ƒ/32

The lens takes 52mm filters, comes standard with a circular-style lens hood, and is available now for around $200.

SharpnessLike most lenses, optimal performance for this lens is achieved when its focal length and aperture are set conservatively in the mid-range. Of course, for a zoom lens, that's not how it's likely to be used by the consumer, so its performance at wide-angle and telephoto is what concerns us. From our tests, optimal (tack-sharp) performance with regard to sharpness is achieved at 80mm and ƒ/11.

Wide open and wide-angle (ƒ/4 & 50mm) the lens is providing acceptable results, with a small sweet spot of sharpness in the middle but significant (4/12 BxU) corner softness. Stopping down to ƒ/5.6 doesn't help, and it's not until ƒ/11 and even ƒ/16 at this focal length that corner softness is mitigated. Zooming in to even 80mm changes the story dramatically; wide open at ƒ/4.5, the lens is almost optimally tack-sharp.

Curiously, our sample of the lens was adverse to ƒ/5.6; performance was always better either a stop below or above.

On the telephoto end, the lens performs well up to about 135mm, after which it begins to soften. Corner softness at 200mm is an issue up to ƒ/11; ƒ/16 produces good results (2/12 BxU), but at this focal length and aperture you're going to need some pretty strong sunlight to light up your subjects. There is a sharp sweet spot between ƒ/5.6-ƒ/11, but corner softness is a factor.

In summary, better than average image sharpness, with noteable corner softness in the extreme (but probably more often used) focal length/aperture combinations.

Chromatic AberrationWe've seen better control of chromatic aberration, but thankfully the worst of it is confined to the corners. Average CA presence hovers around 3/100ths of a percent of frame height throughout the image, but in the corners it can get as high as 8/100ths when used at 95mm and ƒ/5.6. CA seems to be present more in the middle focal lengths and wider apertures; at telephoto, CA is less severe.

Shading (''Vignetting'')Corner shading is only an issue for this lens when set to an aperture between ƒ/4 and ƒ/5.6. Even then, the worst result is a half-stop darker in the corners than the middle (ƒ/4), which isn't that noticeable. By ƒ/8, corner shading is a quarter-stop or less. These results are consistent across all focal lengths.

DistortionDistortion is fairly complex for this lens. At its widest angle the distortion is uniformly barrel, but barely significant; around 0.3% in the corners. By around 65mm the barrel distortion in the corner regions of the image disappears, but as the focal length increases the central distortion turns into the pincushion (''squeeze'') style. By 95mm the pincushion distortion reaches its extreme in the corners, at -0.5%.

This distortion is complicated because after 95mm, the combination of barrel distortion in the center of the image and pincushion in the corners means if you correct for one, you will accentuate the other. Fortunately, the results aren't drastically extreme - 0.5% is noticeable, but not jarring.

Autofocus OperationThe 50-200mm ƒ/4-5.6 focuses relatively slowly, but then this is a mechanically-driven lens that has to push a fair amount of glass around. On a K100D Super, a full focus racks through in 1.3 seconds and is fairly noisy; click here for a recording of the lens focusing. Point-to-point focusing was somewhat sluggish.

Build Quality and HandlingThe Pentax 50-200mm ƒ/4-5.6 is fairly solidly built for a consumer-level lens, with a metal lens mount but plastic filter threads. The zoom ring is fairly hefty, a beefy plastic ribbed texture that's about an inch wide and very easy to grab on to. A quarter clockwise turn takes you through the entire focal range, and the transition between marked lengths is linear, so composition is very easy. Because the lens is so light, zoom creep isn't a factor with casual use, but I found if I gave the body a healthy shaking the zoom would extend. Extending the focal length to 200mm adds about 70% to the overall length of the lens; focusing to infinity adds another 30%, effectively doubling the length of the lens.

Manual focusing is a breeze, thanks to Pentax's quick-shift system, which lets you override autofocus by simply turning the focus ring whenever you like. The focus ring travels through 180 degrees, giving lots of room for effective manual focusing. A distance scale is etched into the focus ring in both feet and meters, and the ring itself is finely ridged and about a quarter-inch wide. There's just a hint of resistance, making it a rare occasion that you'll accidentally bump your focus off. While the lens does extend while focusing, the front filter ring doesn't rotate during focusing or zooming, which is essential for easy use of polarizing filters.

Pentax makes using a polarizer even easier with their lens hood design, which lets you remove a section to have access to the polarizer and still use the lens hood. The circular-style hood is fairly beefy itself, about an inch and a half long, and it does reverse and attach solidly to the lens for easy storage, but affixing it this way makes it practically impossible to use the zoom or focus rings. In practice, it works well to control flare, which is more of a problem with the sun hitting at oblique angles rather than directly.

Alternatives

Pentax 75-300mm ƒ/4.5-5.8 AL SMC P-FA J ~$120As a J-series lens, the 75-300mm offers a bit longer reach at both ends, and is only slightly slower. Optically the 50-200mm is a bit sharper, they both have their issues with CA, but the 75-300mm has less vignetting and distortion. The 75-300mm is also a full-frame lens, but the J-series monicker means it's a lower-quality lens; for example, attached filters rotate during focusing, and there's no aperture ring.

Pentax 55-300mm ƒ/4-5.8 ED SMC DA ~400A fairly new offering from Pentax, we haven't yet tested it, but it seems to offer a longer telephoto end at the expense of the tiniest bit of maximum aperture.

Pentax 50-135mm ƒ/2.8 ED AL IF SDM SMC DA* ~$780One of Pentax's high-end DA* lenses, this is the premium offering in the mid-range telephoto zoom category; its highlight is the constant ƒ/2.8 aperture, for which you pay a premium price.

Sigma 55-200mm ƒ/4.5-5.6 DC ~$140The only third-party product available in the same range on a Pentax K-mount, we haven't tested this lens but optically it is a similar layout (although the Pentax version seems to use better lens elements.

ConclusionI'd say this lens gives the consumer good value for the money, with a better-than-average test result for sharpness. In the right circumstances (ie., 80mm and ƒ/8-11) sharpness results are excellent, but this does limit the lens to applications with strong natural or additional lighting. Chromatic aberration tolerance is fair, vignetting is good, and as is typical for telephoto zooms, distortion is a bit complicated but but not extremely noticeable. For the price tag, we've seen a lot worse results, so you have to hand it to Pentax: they've produced a good lens for a very reasonable price.

Sample Photos

The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.

As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.

If you want a low-cost, small, and/or lightweight zoom for this range, then this is the perfect lens. The image quality isn't the greatest, but is as good as one could expect at this price and weight. I got it because I wanted a telephoto zoom that I would be able to take on long hiking trips where weight was an issue, and I was on a tight budget. This lens fit those criteria and I'm very pleased with it overall.

I bought this lens as a cheap way to cover the 100-200mm range and the 1:4 macro, not expecting much from it in the image quality department. I was very surprised by how well it performs, even at 200mm. Images are much shaper than I expected and the bokeh is not bad either. I haven't really used the 50mm side as I have primes in that range.

This a great zoom lens to use with the Pentax DSLRs. It's small and lightweight, inexpensive and gives good reults overall. It's a little slow and not the best near wide open, but I'm very glad it's in my camera bag. It's a little plasticky felling for my tastes, but it seems to be holding up fine.

Metal lens Mounts. Large rubber zoom ring. Quiet, quick & accurate auto focus. Quality of photographs very high for a kit lens and are comparable to much more expensive pro caliber zoom lenses. Good close focusing distance for macro shots (39.5" to 42.5" aprox) Quick shift AF/MF mechanism. For the price this lens is a steal!

This lens is a perfect companion to the 18-55mm kit lens. The price is not a good indicator of the performance of this lens. It is very light, compact and provides great optics. Its a little short on the 50mm end for a perfect walk-around lens, but it comes close. Great value for the money - highly recommend picking this lens up.